Is there a list somewhere of which specs/classes are best for which bosses?

If you play the game enough, you'll figure out eventually which specs you prefer to run on each boss. Typically a good rule of thumb is if the boss is mostly stationary (or if tanks can work well with an Engi/Sabo Sniper/Slinger), and if adds are frequent, then it's probably a good fight for this spec. There are I think 46 Operation Bosses (not including World Bosses or the other single instanced ones), so creating a list that long would take a little bit of time. I probably wouldn't be able to do it because I don't really know how well each spec is performing against the others (I know Engi is #1, but idk where Marksman and Virulence stand against each other), but someone who plays sniper a little bit more frequently might be interested in making one.

"We have winnowed all futures. The cull endures. It is optimal. It is necessary." - Shiva

If you play the game enough, you'll figure out eventually which specs you prefer to run on each boss. Typically a good rule of thumb is if the boss is mostly stationary (or if tanks can work well with an Engi/Sabo Sniper/Slinger), and if adds are frequent, then it's probably a good fight for this spec. There are I think 46 Operation Bosses (not including World Bosses or the other single instanced ones), so creating a list that long would take a little bit of time. I probably wouldn't be able to do it because I don't really know how well each spec is performing against the others (I know Engi is #1, but idk where Marksman and Virulence stand against each other), but someone who plays sniper a little bit more frequently might be interested in making one.

One could look at the parsley operations leaderboards for a quick overview of which spec has the biggest numbers between each fight. Only caveat being that if your tanks want to move too much you may be personally do better with MM or Viru than Engi even if it pulls the highest numbers.

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The statements and opinions expressed on these websites are solely those of their respective authors and do not necessarily reflect the views, nor are they endorsed by Bioware, LucasArts, and its licensors do not guarantee the accuracy of, and are in no way responsible for any content on these websites.